Flow circuitry and valving for reversible hvac heat exchange configurations

ABSTRACT

An HVAC system can include a multiport valve for controlling refrigerant circulation that permits refrigerant flow in a first direction through an interior heat exchanger and in a first direction through an auxiliary heat exchanger and at least one additional configuration in which refrigerant flows in a second direction through at least one of the interior heat exchanger and the auxiliary heat exchanger. The at least one configuration can include a second configuration in which refrigerant flows in the first direction through the interior heat exchanger and in the second direction through the auxiliary heat exchanger and a third configuration in which refrigerant flows in the second direction through the interior heat exchanger and the auxiliary heat exchanger.

BACKGROUND

Heating, ventilation, and air conditioning (HVAC) systems are employed in a wide variety of climate control applications. In at least some such applications, it may be desirable to provide a multiplicity of climate control functions for the same space at different times, such as heating the space, cooling the space, and dehumidifying the space. Some applications may present unique challenges in this regard, for example, relating to packaging, capacity, complexity, and performance.

SUMMARY

Disclosed herein are exemplary HVAC systems, components, and operational techniques that may be advantageously employed to provide improved HVAC systems and operation.

An HVAC system can include an interior heat exchanger that receives an air stream, facilitates heat transfer between the air stream and a refrigerant, and discharges the air stream; an auxiliary heat exchanger that receives the air stream discharged from the interior heat exchanger and facilitates further heat transfer between the air stream and the refrigerant, and dischargers the air stream; and a multiport valve that controls refrigerant circulation through the interior heat exchanger and the auxiliary heat exchanger. The multiport valve can have a first configuration in which refrigerant flows in a first refrigerant flow direction through the interior heat exchanger and in a first refrigerant flow direction through the auxiliary heat exchanger, wherein the first refrigerant flow direction is a cross-counter flow direction relative to airflow through a respective heat exchanger. The multiport valve can have at least one additional configuration in which refrigerant flows in a second refrigerant flow direction through at least one of the interior heat exchanger and the auxiliary heat exchanger, wherein the second refrigerant flow direction is a cross-parallel flow direction relative to airflow through the respective heat exchanger.

The at least one configuration in which refrigerant flows in a second refrigerant flow direction through at least one of the interior heat exchanger and the auxiliary heat exchanger can further include a second configuration in which refrigerant flows in the first refrigerant flow direction through the interior heat exchanger and in the second refrigerant flow direction through the auxiliary heat exchanger and a third configuration in which refrigerant flows in the second refrigerant flow direction through the interior heat exchanger and the auxiliary heat exchanger. The first configuration can be a heating configuration, the second configuration can be a dehumidifying configuration, and the third configuration can be a cooling configuration. In the first/heating configuration refrigerant can flow first through the auxiliary heat exchanger and then through the interior heat exchanger, and in the third/cooling configuration refrigerant can flow first through the interior heat exchanger and then through the auxiliary heat exchanger. The multiport valve can further have at least one configuration in which refrigerant flow bypasses at least one of the interior heat exchanger and the auxiliary heat exchanger.

A multiport valve for controlling refrigerant circulation through an interior heat exchanger and an auxiliary heat exchanger of an HVAC system can include a first configuration that permits refrigerant flow in a first refrigerant flow direction through the interior heat exchanger and in a first refrigerant flow direction through the auxiliary heat exchanger and at least one additional configuration in which refrigerant flows in a second refrigerant flow direction through at least one of the interior heat exchanger and the auxiliary heat exchanger. The at least one configuration in which refrigerant flows in a second refrigerant flow direction through at least one of the interior heat exchanger and the auxiliary heat exchanger can include a second configuration in which refrigerant flows in the first refrigerant flow direction through the interior heat exchanger and in the second refrigerant flow direction through the auxiliary heat exchanger and a third configuration in which refrigerant flows in the second refrigerant flow direction through the interior heat exchanger and the auxiliary heat exchanger.

The multiport valve can have at least six ports. In the first configuration a hot gas port can be coupled to a first port of the auxiliary heat exchanger, a second port of the auxiliary heat exchanger can be coupled to a first port of the interior heat exchanger, and a second port of the interior heat exchanger can be coupled to a liquid refrigerant line of the HVAC system. The first configuration can be a heating configuration. In the second configuration, a hot gas port can be coupled to a first port of the auxiliary heat exchanger, a suction line can be coupled to a second port of the auxiliary heat exchanger, a liquid refrigerant line can be coupled to a first port of the interior heat exchanger, and a second port of the interior heat exchanger can be coupled to an expansion valve of the HVAC system, thereby reversing refrigerant flow through the interior heat exchanger relative to the first configuration while maintaining refrigerant flow in the first refrigerant flow direction through the auxiliary heat exchanger. The second configuration can be a dehumidifying configuration. In the third configuration, a second port of the interior heat exchanger can be coupled to an expansion valve of the HVAC system, a first port of the interior heat exchanger can be coupled to a second port of the auxiliary heat exchanger, and a first port of the auxiliary heat exchanger can be coupled to a suction line, thereby reversing refrigerant flow through the interior heat exchanger and the auxiliary heat exchanger relative to the first configuration. The third configuration can be a cooling configuration.

The multiport valve can further have at least one configuration in which refrigerant flow bypasses at least one of the interior heat exchanger and the auxiliary heat exchanger.

A method of operating an HVAC system to achieve a plurality of operating modes can include: actuating a multiport valve to a first position corresponding to a first operating mode, the first position permitting refrigerant flow in a first refrigerant flow direction through an interior heat exchanger that also receives an airstream from an interior space and in the first refrigerant flow direction through an auxiliary heat exchanger that receives the airstream from the interior heat exchanger and returns it to the interior space; actuating the multiport valve to at least one other position corresponding to at least one other operating mode, the at least one other position reversing refrigerant flow to a second refrigerant flow direction through at least one of the interior heat exchanger and the auxiliary heat exchanger. Actuating the multiport valve to at least one other position corresponding to at least one other operating mode, the at least one other position reversing refrigerant flow to a second refrigerant flow direction through at least one of the interior heat exchanger and the auxiliary heat exchanger, can further include actuating the multiport valve to a second position corresponding to a second operating mode, the second position reversing refrigerant flow through the interior heat exchanger and actuating the multiport valve to a third position corresponding to a third operating mode, the third position reversing refrigerant flow through the interior heat exchanger and the auxiliary heat exchanger. The first operating mode can be a heating mode, the second operating mode can be a dehumidifying mode, and the third operating mode can be a cooling mode. The first refrigerant flow direction can be a cross-counter flow direction relative to airflow through a respective heat exchanger and reversed refrigerant flow can be in a cross-parallel flow direction relative to airflow through a respective heat exchanger.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a block diagram of an HVAC system operating in an air conditioning mode.

FIG. 1B illustrates a block diagram of an HVAC system operating as a heat pump in a heating mode.

FIG. 1C illustrates a block diagram of an HVAC system operating as an air conditioner with an auxiliary heat exchanger for dehumidification.

FIG. 1D illustrates a block diagram of an HVAC system operating as a heat pump in a heating mode with an auxiliary heat exchanger for additional heating.

FIG. 2A illustrates an HVAC system with multiple heat exchangers and a multiport valve in a heat pump heating configuration.

FIG. 2B illustrates an HVAC system with multiple heat exchangers and a multiport valve in a dehumidifying configuration.

FIG. 2C illustrates an HVAC system with multiple heat exchangers and a multiport valve in a cooling configuration.

FIG. 3A illustrates an exemplary multiport valve.

FIG. 3B illustrates an exemplary multiport valve in heating, cooling, and dehumidifying positions.

FIG. 4 illustrates an exemplary multiport valve.

FIG. 5 illustrates an exemplary expansion valve.

FIG. 6A illustrates a heat exchanger in a cross-parallel flow configuration.

FIG. 6B illustrates a heat exchanger in a cross-counter flow configuration.

DETAILED DESCRIPTION

In the following description, for purposes of explanation, numerous specific details are set forth to provide a thorough understanding of the disclosed concepts. As part of this description, some of this disclosure's drawings represent structures and devices in block diagram form for sake of simplicity. In the interest of clarity, not all features of an actual implementation are described in this disclosure. Moreover, the language used in this disclosure has been selected for readability and instructional purposes, has not been selected to delineate or circumscribe the disclosed subject matter. Rather the appended claims are intended for such purpose.

Various embodiments of the disclosed concepts are illustrated by way of example and not by way of limitation in the accompanying drawings in which like references indicate similar elements. For simplicity and clarity of illustration, where appropriate, reference numerals have been repeated among the different figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth to provide a thorough understanding of the implementations described herein. In other instances, methods, procedures, and components have not been described in detail so as not to obscure the related relevant function being described. References to “an,” “one,” or “another” embodiment in this disclosure are not necessarily to the same or different embodiment, and they mean at least one. A given figure may be used to illustrate the features of more than one embodiment, or more than one species of the disclosure, and not all elements in the figure may be required for a given embodiment or species. A reference number, when provided in a drawing, refers to the same element throughout the several drawings, though it may not be repeated in every drawing. The drawings are not to scale unless otherwise indicated, and the proportions of certain parts may be exaggerated to better illustrate details and features of the present disclosure.

As illustrated in FIGS. 1A-1D, HVAC systems may operate on vapor compression principles that are known to those ordinarily skilled in the art. Such systems can include a compressor 112 that compresses a working fluid, described herein as a refrigerant. The refrigerant can be any of a variety of fluids. Historically these included various fluorocarbon compounds, although there has been a long-term trend in HVAC systems toward more environmentally friendly refrigerants, including carbon dioxide. Any of a variety of fluids may be used, which determine the various operating temperatures and pressures of the system. The compressed refrigerant can be passed to an external heat exchanger 114, which may act as a condenser when the system is in an air conditioning mode. The condenser can take the warm, vapor phase refrigerant and cool it, transferring heat to an outside environment 102 (i.e., outside the interior space 101 in which the air is being conditioned). This can also cause the refrigerant phase to change to a liquid. Liquid refrigerant can then pass through an orifice or expansion valve 116, which causes a further phase change, back to a vapor, with a corresponding reduction in temperature. This cooled refrigerant can pass through an interior heat exchanger 118, located in interior space 101. Interior air can also be passed through interior heat exchanger 118, thereby cooling the interior air by transferring heat therefrom to the refrigerant (raising the refrigerant temperature). The warmed, vapor phase refrigerant then returns to the compressor, which compresses it, and the cycle repeats. By this cycle, heat can be transferred from the air in interior 101 to the exterior environment 102, carried by the refrigerant. The system may also include other components, such as additional heat exchangers, accumulators, dryers, etc., although such components are not necessarily material to the concepts described herein. Additionally, there may be fans, ducts, and other airflow components located both in the interior 101 and exterior space 102 to facilitate airflow across/through the respective heat exchangers to accomplish the above-described functions. In some applications, heat exchange may take place via a secondary loop, e.g., a glycol-water loop. Also, in some applications, for example dehumidifying appliances, portable air conditioners, etc., the “interior” and “exterior” designations may be more fluid as they may be in the same space but have isolated airflow or other arrangements to permit their intended function.

Some HVAC systems, for example automotive HVAC systems, may also include an auxiliary interior heat exchanger 120. In conventional automobile HVAC systems, this interior heat exchanger 120 may be a heater core, through which engine coolant warmed by waste heat from an internal combustion engine may be passed. In such systems, the above-described vapor compression system may be used for cooling, while the auxiliary heat exchanger may be used for heating. In some cases, such as dehumidifying (e.g., defogging windows), both systems may be operable simultaneously as further described below with reference to FIG. 1C.

FIG. 1A illustrates a block diagram of an HVAC system operating in an air conditioning mode. As described above, compressor 112 compresses the refrigerant and delivers hot gas via line 113 to external heat exchanger (condenser) 114. External heat exchanger (condenser) 114 cools the refrigerant and condenses it, dumping the heat into exterior environment 102. The liquid refrigerant passes via refrigerant line 115, through expansion valve 116, which provides a pressure drop resulting in a phase change and temperature reduction. The cooled, vapor refrigerant passes through refrigerant line 117 to interior heat exchanger 118, which acts as an evaporator. Interior heat exchanger 118 is located within interior 101, and interior air flow 106 may also pass through interior heat exchanger (evaporator) 118, cooling the interior air by putting its heat into the refrigerant. Warmed refrigerant may return via line 119 to the compressor, allowing the cycle to repeat.

FIG. 1B illustrates a block diagram of an HVAC system operating as a heat pump in a heating mode. In some cases, a cooling system as described above may be operated with the refrigerant flow reversed. Such systems are described as “heat pumps,” as they serve to pump heat from one side to the other. This allows the system to be used to heat the interior air as well as cool it. In the heat pump's heating mode shown in FIG. 1B, refrigerant flow is reversed so that compressor 112 discharges hot, vapor phase refrigerant via line 119 to interior heat exchanger 118, which now operates as a condenser. Interior air 106 can also be passed through interior heat exchanger 118, warming the interior air by extracting heat from the refrigerant. The cooled refrigerant passes via line 117 to expansion valve 116, where it can undergo a pressure change resulting in a temperature drop and phase change. The cooled vapor refrigerant then passes via line 115 to exterior heat exchanger 114, which now operates as an evaporator. The chilled refrigerant can absorb heat from the outside environment 102, returning refrigerant via line 113 to compressor 112 allowing the cycle to repeat.

FIG. 1C illustrates a block diagram of an HVAC system operating as an air conditioner with an auxiliary heat exchanger for dehumidification. FIG. 1C illustrates an arrangement like the arrangement of FIG. 1A, with the inclusion of auxiliary heat exchanger 120. The refrigerant flow is as described above with respect to FIG. 1A, meaning that the system is operating in a cooling mode. Auxiliary heat exchanger may be used as part of a reheat function, e.g., dehumidification, such as might be used when defogging windows in an automotive application. More specifically, auxiliary heat exchanger may have a heated working fluid passing therethrough. Interior airflow 106 can be passed over internal heat exchanger (evaporator) 118 to cool the airflow. This cooling can include both sensible cooling, which lowers the temperature, and latent cooling, which removes moisture from the air, i.e., reduces the absolute humidity. The cooled air may be passed through auxiliary heat exchanger 120 (e.g., a heater core) to reheat it, raising the temperature thereby decreasing the relative humidity.

FIG. 1D illustrates a block diagram of an HVAC system operating as a heat pump in a heating mode with an auxiliary heat exchanger for additional heating. FIG. 1D illustrates an arrangement like the arrangement of FIG. 1B, with the inclusion of auxiliary heat exchanger 120. The refrigerant flow is as described above with respect to FIG. 1B, meaning that the system is operating in a heating mode. Auxiliary heat exchanger may be used as part of a supplemental heat function, such as might be used in extremely cold conditions. More specifically, auxiliary heat exchanger may have a heated working fluid passing therethrough. In any case, interior airflow 106 can be passed over internal heat exchanger (evaporator) 118 to heat the airflow. The (partially) heated air may be passed through auxiliary heat exchanger 120 (e.g., a heater core) to further heat it. This arrangement can allow for greater heating capacity, for example as might be used in very cold conditions.

The above description is provided primarily for context. Many variations on these concepts might be used in given system. For example, depending on the refrigerant, working temperatures, and working pressures, the “condenser” coil might not actually cool the refrigerant sufficiently to induce a phase change. In such applications, “gas cooler” might be a more appropriate term than “condenser,” although the basic heat transfer arrangement described above would still apply. Similarly, the liquid to vapor phase change associated with the expansion valve and/or evaporator may occur at different points in the loop and/or may not occur at all in certain conditions. In such condition “evaporator” may not be the most precise term for the cold side heat exchanger. Nonetheless, such terms are in wide use in the art, and are used here as an aid to understanding.

FIGS. 2A-2C illustrate a portion of an HVAC system having two heat exchangers facilitating heat transfer with the air to be conditioned, i.e., an interior heat exchanger 318 and an auxiliary heat exchanger 320, along with a multiport valve 325 that allows for reversible operation of both heat exchangers in various operating modes. More specifically, multiport valve may be considered as having (at least) three positions that route refrigerant for heating, dehumidifying, and cooling operations as described in greater detail below. In some configuration an expansion valve may be implemented as a separate component (as shown in FIGS. 2A-2C); however, the expansion valve functionality may also be provided within multiport valve 325 as a single component. FIG. 2A illustrates interior heat exchanger 318 and auxiliary heat exchanger 320 with multiport valve 325 in a heating configuration 300 a. The compressor and expansion valve have been omitted for clarity but can operate as generally described above with respect to FIGS. 1B & 1D for heat pump heating. Interior airflow 106 can pass first through the fins of interior heat exchanger 318 and then through the fins of auxiliary heat exchanger 320. Heated refrigerant from the compressor can be routed by multiport valve 325 to a first port 321 of auxiliary heat exchanger 320. The refrigerant can pass through the tubes of auxiliary heat exchanger 320, exiting via port 322, and returning to multiport valve 325. Refrigerant can then pass from multiport valve 325 to a first port 323 of interior heat exchanger 318, through the tubes of interior heat exchanger 318, exiting via port 324 and returning to multiport valve 325, which can then route refrigerant to the exterior heat exchanger (not shown in FIG. 2A) and back to the compressor (not shown in FIG. 2A).

In the illustrated heating configuration, air and refrigerant flow through both interior heat exchanger is in a cross-counter flow configuration, which is illustrated in greater detail in FIG. 6B. Air to fluid heat exchangers may be constructed from a plurality of cooling fins 741 through which a plurality of fluid tubes pass perpendicularly. As a result, the air flows through the fins “across” the fluid tubes, providing what can be described as a “cross” flow. Additionally, depending on the direction of fluid flow in the tubes relative to the direction of the airflow, this crossflow can be cross-counter flow or cross-parallel flow. Cross-counter flow means that the net direction of the zig-zagging fluid flow path 744 is counter to the direction of the air flow, as illustrated in cross-counter flow configuration 740 b of FIG. 6B. The net fluid flow direction 744 is upward on the page, zigzagging back and forth to the left and right. In other cases, the same heat exchanger construction can be operated to provide cross-parallel flow, as illustrated in FIG. 6A. This can be achieved by reversing the fluid flow direction through the heat exchanger, such that the net of the zigzagging fluid flow path 743 is parallel to the direction of the air flow, as illustrated in cross-parallel flow configuration 740 a of FIG. 6A, in which the net fluid flow direction is downward on the page, zigzagging back and forth to the left and right. In the context of the illustrations of FIGS. 6A-6B, left, right, up, down, etc. merely refer to the directions in the depiction of the figure and can be in any orientation in a physical implementation.

In at least some embodiments, a cross-counter flow configuration may provide more effective operation in heating modes via improved heat transfer. Thus, it may be desirable for the configurations illustrated in FIGS. 2A-2C to provide for cross-counter flow for each heat exchanger used as a heater, as illustrated for heat exchangers 318 and 320 in FIG. 2A and for heat exchanger 320 in FIG. 2B. Conversely, when a heat exchanger is used in a cooling mode, a cross-parallel flow may be used, as illustrated with heat exchanger 318 in FIG. 2B and heat exchangers 318 and 320 illustrated in FIG. 2C. This can be because refrigerant in a condenser/gas cooler may undergo a relatively larger temperature change. For example, even though the refrigerant in the evaporator is absorbing heat, its temperature may be decreasing for much if its time in the heat exchanger because its pressure is dropping. With conventional refrigerants, the temperature may increase significantly once all the liquid is evaporated. Such systems may meter refrigerant flow rate based on this temperature increase using a thermostatic expansion valve (TXV); however, in a carbon dioxide system or other system using subcooling control, the outlet of the evaporator can be a two-phase (liquid and gas) system. In such a system, the refrigerant temperature may not increase at any point in the heat exchanger. Thus, for the embodiments described herein, it may be preferable to provide cross-counter flow operation in the heating modes because it can increase the log-mean temperature difference. For an evaporator without superheat, such concerns may be less relevant, but there may be a slight heat transfer advantage to parallel flow.

FIG. 2B illustrates interior heat exchanger 318 and auxiliary heat exchanger 320 with multiport valve 325 in a dehumidifying configuration 300 b. The compressor has been omitted for clarity, but system operation is similar to that described above with respect to FIGS. 1A and 1C for cooling operations. Interior airflow 106 passes first through the fins of interior heat exchanger 318, which cools the air and removes moisture, e.g., by condensation onto interior heat exchanger (evaporator) 318. Interior airflow 106 can then also pass through the fins of auxiliary heat exchanger 320. Heated refrigerant from the compressor can be routed by multiport valve 325 to a first port 321 of auxiliary heat exchanger 320. The refrigerant can pass through the tubes of auxiliary heat exchanger 320, exiting via port 322, and returning to multiport valve 325. (As noted above, this occurs in a cross-counter flow mode.) From multiport valve 325, the refrigerant can pass to a second port 324 of interior heat exchanger 318, via expansion valve 316, through the tubes of interior heat exchanger 318, exiting via port 323 and returning to multiport valve 325, which then routes refrigerant to the back to the compressor (not shown in FIG. 2B). Airflow through interior heat exchanger 318 is in a cross-parallel flow configuration. In summary, multiport valve 325 in the dehumidifying configuration can reverse flow through interior heat exchanger 318 (as compared to the heating configuration).

FIG. 2C illustrates interior heat exchanger 318 and auxiliary heat exchanger 320 with multiport valve 325 in a cooling configuration 300 c. The compressor has been omitted for clarity, but the system operates in a way broadly similar to that described above with respect to FIGS. 1A and 1C for cooling operations. Interior airflow 106 passes first through the fins of interior heat exchanger 318, which cools the air and removes moisture, e.g., by condensation onto interior heat exchanger (evaporator) 318. Interior airflow 106 can then also pass through the fins of auxiliary heat exchanger 320, which can further cool the air. Heated/compressed refrigerant from the compressor can be routed through an exterior heat exchanger (condenser) (not shown in FIG. 2C) and then to multiport valve 325. From multiport valve 325, refrigerant can pass through expansion valve 316 to second port 324 of interior heat exchanger 318. Refrigerant can pass through heat exchanger 318 in a cross-parallel flow configuration, returning to multiport valve 325 via exit port 323. Refrigerant flow can then continue from multiport valve 325 to auxiliary heat exchanger 320 via port 322. Refrigerant can then pass through heat exchanger 320 in a cross-parallel flow configuration, returning to multiport valve 325 via port 321 of auxiliary heat exchanger 320. From multiport valve 325, refrigerant can return the compressor (not shown in FIG. 2C). In summary, multiport valve 325 in the cooling configuration can reverse flow through interior heat exchanger 318 and auxiliary heat exchanger 320 (as compared to the heating configuration).

Variations of the above-described modes are also possible. For example, in some cases an alternative or additional cooling mode could be configured in which auxiliary heat exchanger is bypassed, providing only one interior heat exchanger/evaporator for the cooling operation. In other cases, an additional or alternative heating mode could be provided in which one of interior heat exchanger 318 or auxiliary heat exchanger 320 is bypassed. Likewise, the dehumidification mode may additionally or alternatively use or bypass the exterior heat exchanger (not shown in FIGS. 2A-2C).

FIG. 3A illustrates an exemplary multiport valve 425, and FIG. 3B illustrates the exemplary multiport valve in heating position 425 a, cooling position 425 c, and dehumidifying position 425 b. As illustrated, the valve may employ a sliding mechanism, but rotational mechanisms or other suitable structural/mechanical configurations may be used. Multiport valve 425 can be an electromechanical device that regulates refrigerant flow responsive to electrical or electronic signals. Refrigerant valves can regulate flow by changing the size of an orifice (including by fully restricting the orifice). There are a variety of mechanisms that can change the orifice size including stepper motors, shape memory alloys, or via an electronically controlled pilot valve. Valves can also be divided based on how integral the housing is to the valve functionality. In certain valves, the valve block is integral to its function while in others the valve is considered a cartridge which is installed inside another device or block. Any of a variety of valve mechanisms can be employed to open/close/restrict the respective orifices, including slider or rotating mechanisms. FIGS. 3A and 3B schematically depict a valve that could be constructed from any of a variety of configurations.

FIG. 3A schematically depicts the structure of an exemplary multiport valve 425. An upper “path” of the valve as illustrated in FIG. 3A can selectively couple a hot gas line (e.g., a compressor discharge line) or a suction line (e.g., a compressor inlet line) to port 321, which can be the first port of auxiliary heat exchanger 320 as discussed above with reference to FIGS. 2A-2C. The middle flow paths in FIG. 3A can selectively couple a liquid refrigerant line (e.g., a condenser outlet) and/or a suction line to port 322 and/or port 323, i.e., the second port of auxiliary heat exchanger 320 and first port of interior heat exchanger 318 as discussed above with reference to FIGS. 2A-2C. The lower path as illustrated in FIG. 3A can selectively couple port 324, which can be the second port of interior heat exchanger 318 as depicted in FIGS. 2A-2C above with a liquid refrigerant line.

With reference to FIG. 3B, a heating configuration 425 a of multiport valve 425 can couple a hot gas line (e.g., compressor discharge) to port 321, a liquid line to port 324, and provide a jumper path between ports 322 and 323, as described above with respect to FIG. 2A. The liquid line can route the liquid refrigerant to an exterior coil acting as an evaporator via an expansion valve. In the dehumidifying configuration 425 b, multiport valve 425 can reverse refrigerant flow through interior heat exchanger 318 relative to the heating configuration while maintaining the same refrigerant flow direction through auxiliary heat exchanger 320, relative to the heating configuration, as described above with respect to FIG. 2B. This can be achieved by decoupling ports 322 and 323, connecting the liquid refrigerant path to port 323, and connecting the suction path to port 322. In the cooling configuration 425 c, multiport valve 425 can reverse refrigerant flow through interior heat exchanger 318 and auxiliary heat exchanger 320 relative to the heating configuration, as described above with respect to FIG. 2C. This can be achieved by decoupling the hot gas line, coupling port 321 to the suction path, providing a jumper path connecting ports 322 and 323, and coupling the liquid refrigerant line (from the condenser) to port 324.

FIG. 4 illustrates an exemplary multiport valve more generally. In configuration 525 a, the multiport valve can have six ports 531 a-531 f. These ports can be connected to the hot gas, suction, liquid lines, and heat exchanger ports 321, 322, and 323, respectively, as depicted above. In the first configuration 525 b, port 531 a can be connected to 531 d, port 531 b can be connected to port 531 e, and port 531 c can be connected to port 531 f This can provide the “straight through” flow paths 532. Configuration 525 b can correspond to the dehumidifying configuration described above. In second configuration 525 a, port 531 a can be coupled via flow path 532A to port 531 d, and ports 531 e and 531 f can be coupled, corresponding to the heating configuration discussed above. In third configuration 525 c, port 531 b can be coupled to port 531 d, via flow path 534 a, and ports 531 e and 531 f can be coupled, via flow path 534 b. This corresponds to the cooling configuration discussed above. It should be noted that each of these configurations can allow for bidirectional flow along the respectively established fluid flow paths.

FIG. 5 illustrates an exemplary expansion valve that can be used in the various configurations below. An expansion valve can have a plurality of configurations, including a first configuration 616 a, in which flow between a first port 631 a and a second port 631 b is blocked (illustrated by 632). In a second configuration 616 b, flow between ports 631 a and 631 b can be via a restricted flow path 633 that can allow for a pressure drop. In some embodiments, multiple restricted states with different degrees of restriction can be provided. The expansion valve can also be configured such that the valve is bidirectional, i.e., presenting the flow restriction in either direction. Finally, in configuration 616 c, the expansion valve can provide an unrestricted flow path 634 between ports 631 a and 631 b. Some HVAC system embodiments including multiple heat exchangers might employ multiple expansion valves, with the expansion valves being operated to provide a restriction when fluid flow is in one direction with respect to the associated heat exchanger(s) and to provide no restriction when fluid flow is in another direction with respect to the associated heat exchanger(s).

The foregoing describes exemplary embodiments of HVAC systems that employ multiple interior heat exchangers and associated valving to allow for reversible refrigerant flow to accommodate various operating modes. Although numerous specific features and various embodiments have been described, it is to be understood that, unless otherwise noted as being mutually exclusive, the various features and embodiments may be combined various permutations in a particular implementation. Thus, the various embodiments described above are provided by way of illustration only and should not be constructed to limit the scope of the disclosure. Various modifications and changes can be made to the principles and embodiments herein without departing from the scope of the disclosure and without departing from the scope of the claims. 

1. An HVAC system comprising: an interior heat exchanger that receives an air stream, facilitates heat transfer between the air stream and a refrigerant, and discharges the air stream; an auxiliary heat exchanger that receives the air stream discharged from the interior heat exchanger and facilitates further heat transfer between the air stream and the refrigerant, and dischargers the air stream; and a multiport valve that controls refrigerant circulation through the interior heat exchanger and the auxiliary heat exchanger, the multiport valve having: a first configuration in which refrigerant flows in a first refrigerant flow direction through the interior heat exchanger and in a first refrigerant flow direction through the auxiliary heat exchanger, wherein the first refrigerant flow direction is a cross-counter flow direction relative to airflow through a respective heat exchanger; and at least one additional configuration in which refrigerant flows in a second refrigerant flow direction through at least one of the interior heat exchanger and the auxiliary heat exchanger, wherein the second refrigerant flow direction is a cross-parallel flow direction relative to airflow through the respective heat exchanger.
 2. The HVAC system of claim 1 wherein the at least one configuration in which refrigerant flows in a second refrigerant flow direction through at least one of the interior heat exchanger and the auxiliary heat exchanger further comprises: a second configuration in which refrigerant flows in the first refrigerant flow direction through the interior heat exchanger and in the second refrigerant flow direction through the auxiliary heat exchanger; and a third configuration in which refrigerant flows in the second refrigerant flow direction through the interior heat exchanger and the auxiliary heat exchanger.
 3. The HVAC system of claim 2 wherein the first configuration is a heating configuration, the second configuration is a dehumidifying configuration, and the third configuration is a cooling configuration.
 4. The HVAC system of claim 3 wherein in the first/heating configuration refrigerant flows first through the auxiliary heat exchanger and then through the interior heat exchanger and in the third/cooling configuration refrigerant flows first through the interior heat exchanger and then through the auxiliary heat exchanger.
 5. The HVAC system of claim 1 wherein the multiport valve has at least one configuration in which refrigerant flow bypasses at least one of the interior heat exchanger and the auxiliary heat exchanger.
 6. A multiport valve for controlling refrigerant circulation through an interior heat exchanger and an auxiliary heat exchanger of an HVAC system, the multiport valve having: a first configuration that permits refrigerant flow in a first refrigerant flow direction through the interior heat exchanger and in a first refrigerant flow direction through the auxiliary heat exchanger; and at least one additional configuration in which refrigerant flows in a second refrigerant flow direction through at least one of the interior heat exchanger and the auxiliary heat exchanger.
 7. The multiport valve of claim 6 wherein the at least one configuration in which refrigerant flows in a second refrigerant flow direction through at least one of the interior heat exchanger and the auxiliary heat exchanger further comprises: a second configuration in which refrigerant flows in the first refrigerant flow direction through the interior heat exchanger and in the second refrigerant flow direction through the auxiliary heat exchanger; and a third configuration in which refrigerant flows in the second refrigerant flow direction through the interior heat exchanger and the auxiliary heat exchanger.
 8. The multiport valve of claim 7 wherein the multiport valve has at least six ports.
 9. The multiport valve of claim 8 wherein in the first configuration a hot gas port is coupled to a first port of the auxiliary heat exchanger, a second port of the auxiliary heat exchanger is coupled to a first port of the interior heat exchanger, and a second port of the interior heat exchanger is coupled to a liquid refrigerant line of the HVAC system.
 10. The multiport valve of claim 9 wherein the first configuration is a heating configuration.
 11. The multiport valve of claim 8 wherein in the second configuration, a hot gas port is coupled to a first port of the auxiliary heat exchanger, a suction line is coupled to a second port of the auxiliary heat exchanger, a liquid refrigerant line is coupled to a first port of the interior heat exchanger, and a second port of the interior heat exchanger is coupled to an expansion valve of the HVAC system, thereby reversing refrigerant flow through the interior heat exchanger relative to the first configuration while maintaining refrigerant flow in the first refrigerant flow direction through the auxiliary heat exchanger.
 12. The multiport valve of claim 11 wherein the second configuration is a dehumidifying configuration.
 13. The multiport valve of claim 8 wherein in the third configuration, a second port of the interior heat exchanger is coupled to an expansion valve of the HVAC system, a first port of the interior heat exchanger is coupled to a second port of the auxiliary heat exchanger, and a first port of the auxiliary heat exchanger is coupled to a suction line, thereby reversing refrigerant flow through the interior heat exchanger and the auxiliary heat exchanger relative to the first configuration.
 14. The multiport valve of claim 13 wherein the third configuration is a cooling configuration.
 15. The multiport valve of claim 6 further having at least one configuration in which refrigerant flow bypasses at least one of the interior heat exchanger and the auxiliary heat exchanger.
 16. A method of operating an HVAC system to achieve a plurality of operating modes, the method comprising: actuating a multiport valve to a first position corresponding to a first operating mode, the first position permitting refrigerant flow in a first refrigerant flow direction through an interior heat exchanger that also receives an airstream from an interior space and in the first refrigerant flow direction through an auxiliary heat exchanger that receives the airstream from the interior heat exchanger and returns it to the interior space; actuating the multiport valve to at least one other position corresponding to at least one other operating mode, the at least one other position reversing refrigerant flow to a second refrigerant flow direction through at least one of the interior heat exchanger and the auxiliary heat exchanger.
 17. The method of claim 16 wherein actuating the multiport valve to at least one other position corresponding to at least one other operating mode, the at least one other position reversing refrigerant flow to a second refrigerant flow direction through at least one of the interior heat exchanger and the auxiliary heat exchanger further comprises: actuating the multiport valve to a second position corresponding to a second operating mode, the second position reversing refrigerant flow through the interior heat exchanger; and actuating the multiport valve to a third position corresponding to a third operating mode, the third position reversing refrigerant flow through the interior heat exchanger and the auxiliary heat exchanger.
 18. The method of claim 17 wherein the first operating mode is a heating mode, the second operating mode is a dehumidifying mode, and the third operating mode is a cooling mode.
 19. The method of claim 18 wherein the first refrigerant flow direction is a cross-counter flow direction relative to airflow through a respective heat exchanger and reversed refrigerant flow is in a cross-parallel flow direction relative to airflow through a respective heat exchanger. 